The Journal of Indian Botanical Society

Respected Dr. Singh, senior botanists of the country and young participants, At the very outset I wish to express my sincere thanks to the Executive Council of Indian Botanical Society for electing me the President of this oldest plant science society of the country.

Callose (cal·lose-kal′ōs′) is wide spread as an important cell wall constituent in a wide variety of plants. It is a plant polysaccharide present in the form of polymer of β-1, 3-glucan linkages with some β-1, 6-branches and it is different from cellulose. Callose has been reported on algae; in the trumpet, the Laminariaceae; in stem hairs of species of Borago, Vitis, Geranium and of Osmunda and Blechnum; in Cuscuta haustoria and in penetrated host cells; in root hairs; in cystoliths in species of the Urticaceae, Moraceae, and Ulmaceae; in pollen-mother cell walls and parenchyma cells in irregular accumulations in an apparently unorganized manner, often result of parasitic attack; in pits of young tracheids; in laticifers of Allium cepa and Hevea brasilliensis; in the endodermis of Equisetaceae and Filicineae; and in pollen grains, pollen tube walls and as plugs in pollen tubes. A substance having the properties of callose was demonstrated under certain conditions in the pits of parenchyma cells. A special callose wall around the zygote functions to preserve the genetic isolation of this cell from maternal and endosperm tissues of different genotype. The callose wall is also surrounding the generative cell in a transitory manner, which breaks down and the generative and vegetative cells are separated by membranes of these cells. Callose is a multiple player in plant growth and development and plays an essential role during pollen development, exine formation, pollen germination, pollen tube growth, fertilization, plasmodesmetal regulation and cell plate formation. The most important function of callose is the formation of exine. Absence or premature dissolution or persistence (lack of dissolution) of callose surrounding the pollen mother cells (PMCs) leads to pollen sterility. Callose surrounding the PMCs provides a template or mould for the formation of the species-specific exine sculpturing pattern. In several species exhibiting sporophytic self-incompatibility, there is complete inhibition of pollen germination on the stigmatic surface. The inhibition or rejection is caused by the deposition of callose in the germ-pore or at the tip of the pollen tube. The stigmatic papillae also produce a lenticular plug of callose at their tips. Abnormalities in pistil development causing low seed-set are known to be due to abnormal patterns of callose deposition.

Callase is synthesized during a variety of processes in plant development and/or in response to multiple biotic and abiotic stresses. It is now generally believed that callose is synthesized by a class of enzymes, termed callose synthases and that it is degraded by β-1, 3-glucanases. Molecular and genetic studies in Arabidopsis have been used to identify a set of genes that are involved in the biosynthesis and degradation of callose. The Arabidopsis genome contains 12 callose synthase (CalS) genes, also known as glucan synthase-like (GSL) genes which encode the catalytic subunit of callose synthesis. In this mini review an attempt has been made to highlight the callose distribution, chemical nature, functions and biosynthesis